The invention pertains to continuous conveyors that are used for transporting large quantities of bulk materials such as sand, stones or ore, as well as for transporting heavy unit loads, for example, in the mining industry such as in open pit mining or deep mining or in the loading and unloading of ships, silos, etc. In this case, the bulk materials or unit loads are loaded onto the tractive transport means in a loading station and transported to an unloading or transfer station.
One typical example of a continuous conveyor is a conveyor belt for carrying off crushed ore. The conveyor belt runs on idlers that are supported in an elongated support construction of steel profiles. In addition to one or more driveshafts, the driving station comprises at least one electric motor that is usually realized in the form of an asynchronous motor and operates with a relatively high speed, e.g., of 1500 rpm. The driving roller that drives the conveyor belt, in contrast, revolves with a relatively slow speed between 5 and 100 rpm. Consequently, a step-down gear needs to be provided between the asynchronous motor and the driving roller, wherein said step-down gear is typically realized in the form of a multi-stage cylindrical gearing or epicyclic gearing and has a reduction ratio between 15:1 and 150:1. Gears with variable transmission ratio are also used in order to adjust the operating speed of the driving roller. The driving motor and, if applicable, the step-down gear may be integrated into the driving roller and realized in the form of a so-called drum motor. The continuous conveyor may also comprise several driving stations such as, e.g., two head stations and one or more intermediate stations, wherein each driving station features one or two electric motors and a corresponding number of driving rollers.
Disruptions during the transport are transmitted in the form of impact loads to the output shaft of the gear via the driving roller and ultimately into the driving motor. Considerable disruptions that are caused, for example, by a backup of bulk material or jamming objects may even lead to the tractive transport means suddenly coming to a brief standstill. However, the rotor of the motor, shafts and toothed wheels of the gear, as well as the driving roller coupled thereto, continue to move due to the significant mass inertia of the overall drive system at least until the motor is automatically shut off or decoupled once certain forces are exceeded. This can lead to considerable mechanical tensions in the gear, the motor and the tractive transport means that result in damages, e.g., tearing, of the tractive transport means. In order to prevent such impermissibly high impact loads and potential damages of the tractive transport means, an overload clutch is frequently installed between the driving roller and the step-down gear in the prior art, wherein this overload clutch automatically engages, i.e. separates the electric drive from the driving roller, when predefined loads above the normal operating loads are exceeded.
Particularly in large and very large continuous conveyors of the type used in the mining industry or in open pit mining, the costs and the expenditure of time required for repairing a torn tractive transport means are so high that this type of damage must be prevented under all circumstances. This results in a correspondingly high constructive effort for the overload clutch and the monitoring and control systems that trigger an emergency shut-off in a timely fashion.